This invention relates generally to systems for identifying military vehicles as friendly or hostile and, more particularly, to identification systems that rely on infrared emissions of the military vehicles.
Friend or foe identification systems used by military aircraft are generally radar-based systems, which operate in the microwave portion of the electro-magnetic spectrum. Because the basic radar return from an aircraft is highly diffracted, the basic return cannot be used to positively identify the shape and, therefore, the type of aircraft. However, other portions of the radar return can be used to identify the type of aircraft. For example, a jet engine modulation (JEM) system analyzes the doppler shift of the radar return to determine the number and rotational velocities of the turbine blades in an aircraft's jet engine. From this, the type of jet engine can be identified and, once the jet engine has been identified, it is usually a simple matter to identify the type of aircraft. However, this system is not reliable as the enemy may be operating the same type of aircraft.
Another friend or foe identification system used by military aircraft utilizes a transponder to encode the radar return with the identity of the vehicle. However, this radar system can also be jammed and, in addition, can be intercepted or mimicked by the enemy. Accordingly, there has been a need for an improved identification system providing rapid and positive friend or foe identification of land, sea and air vehicles at long ranges without the possibility of being jammed, intercepted or mimicked. The present invention clearly fulfills this need.